Perform room unit tests with 'local' users actually in the right domain ;)

synapse/handlers/message.py

@@ -76,6 +76,10 @@ class MessageHandler(BaseRoomHandler):
         Raises:
             SynapseError if something went wrong.
         """
+        # TODO(paul): Why does 'event' not have a 'user' object?
+        user = self.hs.parse_userid(event.user_id)
+        assert(user.is_mine)
+
         if stamp_event:
             event.content["hsob_ts"] = int(self.clock.time_msec())